The present invention relates to a spinnerette for producing mesophase pitch fibers, and particularly to a spinnerette structure for controllably adjusting the fiber structure of the fiber produced.
Producing a carbon fiber from mesophase pitch includes passing mesophase pitch through a channel or bore in a spinnerette, thermosetting the resulting pitch fibers and then carbonizing the pitch fibers to produce carbon fibers.
Carbon fibers produced from mesophase pitch can have different cross-sectional structures which result from crystallite orientation within the fiber. The cross-sectional structure can be viewed under magnification. Such cross-sectional structures are either generally tangential, which is a multilayer annular array of crystals called an "onion skin" structure, or they are generally radial, or they may have a random structure which is neither one nor the other. It is known that a change in the cross-sectional structure of the fiber from more radial to more onion skin increases the tensile strength of the fibers. The carbon fiber cross-sectional structure is determined by the channel or bore through the spinnerette and that structure is preserved after the pitch fiber has been converted to the carbon fiber by carbonization.
The desirability of improving the characteristics of mesophase pitch fiber has been recognized previously, and one technique that has been used for selecting a particular cross-sectional structure for a mesophase pitch fiber is described in U.S. Pat. No. 4,376,747. In that patent, the cross-sectional structure of the carbon fibers is adjusted by positioning a porous body having certain specific properties in the spinnerette channel.